Midterm 1 Flashcards
How did the earth obtain the heat in it’s interior?
From accretion & radioactive decay
What is differentiation/why the interior is layered
The separation of metals and rocks due to density differences
If the inner core is hotter than the outer core, why is only the outer core a liquid?
Inner core is at a higher pressure, and this will shift it into a more dense state, meaning a higher melting point is required relative to the outer core.
What is the cold, strong crust plus the outer, strong part of the mantle called?
Lithosphere
What is warm, weak layer of mantle beneath the rigid plates called?
Asthenosphere
Evidence of continent drifting
- Coastline of America lines up with Europe and Africa’s. Identical volcanic rocks appear on both sides of the Atlantic. Fossil of non-swimmers found in both sides of continents
The Earth’s interior layers and which is thickest/thinnest.
Crust: 0-40km
Mantle: 40 -2890km
Liquid iron outer core: 2890 - 5150km
Solid liquid iron core: 5150 - 6370km
What a solar nebula is?
A cloud of dust and gas particles that are the origin of the solar system.
Where the heat come from that causes new planets to be extremely hot inside.
Planet accretion which comes from ever frequent collisions of rock. These collisions and radioactive elements create the heat that melts the interior.
Plate techtonics
How pieces of a strong lithosphere move around the weak asthenosphere.
Why the inner core is hotter than the outer core yet is a solid.
The inner core has a much greater pressure at the depth closer to the earth’s centre, which results in the core being in a denser state, requiring a greater melting point to turn it into a liquid.
Why hotter mantle beneath the asthenosphere does not flow as easily.
Greater pressure results in a denser state, making it more rigid.
Why few scientists accepted Wegener’s theory of continental drift.
It would require strong oceanic crust to be adjusted for the continents, and the cause of such a strong force would be unknown.
What are Magnetic reversal
Magnetic crystals in lava flow like compasses, showing that the north and south pole switched places.
How we know that our magnetic field has reversed itself many times through Earth’s past.
Changes in polarity over millions of years
The breakthrough observation that led to the theory of plate tectonics.
The magnetic reversals found in oceanic crust seafloor. The ocean crust would form but then move away. This allowed wegner’s theory, to be true as the continents could now drift apart due to ocean crust not being in the way.
Mid-ocean ridge
Magma from far below reaches the surface and cools to form the ocean lithosphere then spreads outwards at the ridge
Subduction zone
Subduction zone is when oceanic plates(excess oceanic crust) is subducted back into the earth’s interior.
Transform plate boundary
A fault where plates slide past each other horizontally
The kind of plate boundary that the San Andreas Fault is.
Transform plate boundary
How plate tectonics may have led to the evolution of whales and dolphins from land mammals.
Over time, as landmasses shifted and environmental pressures changed, certain land mammals, such as the ancestors of whales and dolphins, adapted to aquatic environments, evolving into fully marine species.
How conduction transfers heat.
Conduction transfers heat through the solid through the spread of vibrations on a atomic scale
How convection transfers heat.
Heat transfer through fluid motions of liquids and gases, as well as solids that flow like a liquid.
How radiative heat transfer transfers heat.
There electromagnetic waves through a transparent medium.
The circumstance in which a solid can convect.
If it has a solid liquid structure(crystalline) but can flow like a liquid.
What drives plate tectonics.
Mantle convection, where due to the mid-ocean ridges where magma from below cools into the earth’s lithosphere and spreads out, where eventually in a subduction zone it is sub-ducted back into the earth’s interior.
What causes a magnetic field to be produced.
If the tiny magnetic fields that come from electrons align, a magnetic field will be formed.
How a permanent magnetic is created.
A permanent magnet can be created by temporarily placing a metal(ferromagnetic) into a strong magnetic field
How to make an induced magnetic field generated by an electrical current stronger.
More coils, greater current, more ferromagnetic core
Strong magnetic field for earth’s core
Electrical current from motion of convecting liquid, Spin of earth causing the convection in the outer core, coils spin around iron core
How Earth generates its magnetic field.
Earth’s magnet field acts as a bar magnetic, with the magnetic field lines from the north to south pole.
That the magnetic pole in Earth’s northern hemisphere is actually a south magnetic pole.
Opposite poles attract, so the geographically north pole must be a south magnetic pole to attract the magnet north.
What causes the aurora lights.
Solar wind excites nitrogen and oxygen in the air
How do we know earth is not hollw
Rocks too weak at the higher temperatures and pressure to support voids. Passage of seismic waves show no voids. magnetic field that can only be generated by an liquid iron core. Magnitude of our planet requires a dense continuous interior
The type of volcanic eruption that brings diamonds to the surface
A kimberlite eruption brings the diamonds up to the surface with cooler surrounding rock before the magma can hurt them
About how many total earthquakes of any size occur globally each year.
1.3 million earthquakes
The largest earthquake to occur on Earth over the past 100 years.
Chile 1960 magnitude 9.5
On average, how often large earthquakes (≥M7.5) occur on the San Andreas Fault.
Every 150 years
Where most earthquakes occur.
Japan as the pacific plate gets stuck as it subducts beneath it, and goes though the elastic rebound and stick-slip behaviour.
The concept of elastic rebound.
Elastic rebound is when crush bends like rubber(storing energy) then unbends(releasing energy)
The concept of stick-slip behavior.
Faults remain stuck while energy builds, then sudenly slip when energy is released. It occurs friction and rough spots along the fault(asperities) prevent the fault from sliding until they can become overcome.
What the rough parts of a fault that prevent slippage until they break are called.
Asperities
How we observe the buildup of stress on a fault.
Using a precise gps, which measures surface velocites between quakes to see how the plates move.
The direction Japan moves between and during earthquakes.
Subduction of the plate before pushes Japan to the west, however during the earthquake bcs of the subduction zone.
Where thrust faults occur
Compressional setting(subduction zone), angle along the fault that shortens, 2 sides slide past while in contact
Where normal faults occur
Extensional setting(mid-ocean ridges), angle along the fault that extends, 2 sides slide past while in contact
Where transform faults occur
Laterally sliding(transform plate boundary), vertical slide, no extension or shorten, 2 sides slide past while in contact
That faults do not open gaps during earthquakes.
The 2 sides always slide each other while remaining in contact.
What an earthquake hypocenter is.
Location at the depth at which the earthquake started
The different types of seismic waves.
2 body waves, P & S. 2 seimic waves, Love and Rayleigh
Characteristics of P-waves
Push-pull motion(compression and expansion), travels through solids, liquids and gases, fastest
Characteristics of S-waves
Side-side motion, travels only through solids, slower than P-waves
Characteristics Love waves
Side-side motion, travels only along solids, slowest to arrive but causes most shaking
Characteristics Rayleigh waves
Up-down motion, travels only along solids, slowest to arrive but causes most shaking
How seismograms are used to locate an earthquake.
Seismograms measure the ground’s motion during an earthquake
What reflection seismology allows us to visualize.
Shows us the shallow crystalline structure of depths a few kilometres below the earth’s surface
What earthquake seismology allows us to visualize.
Shows us deep structures through the earth’s interior, such as subducting plates and the earth’s core; Higher density - blue, lower dnsity-red
How we know that the outer core of the Earth is liquid.
The reflection of p-waves must have traveled through the earth’s core, with the seismogram returning a lower density(red).
How much the amount of shaking varies between different magnitude earthquakes.
1 greater magnitude, 10 times greater shaking
That smaller magnitude earthquakes occur more often.
Less shaking and less of an elastic rebound/stick-slip behaviour is required
The theoretical maximum magnitude earthquake that can occur.
Around 10 min magnitude
The relationship between the magnitude of an earthquake and its duration.
The greater the magnitude, the more it shakes.
What is earthquake shaking caused by?
Rubbing of the 2 sides of the fault as the rupture propagates, which generates seismic waves, which travel below to the earth’s interior.
The influence of geology on earthquake shaking.
More unconsolidated sediments make the area weaker. They lack cohesive strength, so when the sesiemic waves pass through them, they slow down and amplify, increasing shaking
What Mercalli intensities measure.
They measure the quantity of the shaking the people and buildings face, which is influenced by the magntiude of the earthquake.
What Mercalli intensities enable us to infer about earthquakes.
Infer the magnitude of historic earthquakes
Why the US Geological Survey believes there is a high seismic hazard in the midwest.
There are a great amount of historic earthquakes in the region
That there are active faults in Indiana.
There are active faults near the new madrid plate because of a rift 500 million years ago caused by the abrupt stop of continents drifting away
That the biggest magnitude earthquakes are generally not the deadliest.
The deadliest earthquakes are the M7-8 quakes in heavily populated regions with poor building practices
The timeframe we can be 90% sure that a large earthquake will occur on a particular fault.
Within several centuries
Why earthquakes are so difficult to predict.
The factors that affect earthquakes are chaotic and unpredictable. We also cannot measure stress level on faults, and stress required for an earthquake.
That there are no reliable earthquake precursors.
There are some somewhat identifiable precursors like foreshocks, surface motion and changes in groundwater, there are no reliable precursors to predict earthquakes.
What instrumentation showed just before the 2004 Parkfield earthquake.
No surface motion before the quake, which contradicted previous theories
The difference between foreshocks and aftershocks.
Foreshocks are the smaller earthquakes/shaking before, aftershocks are the smaller earthquakes/shaking after.
That a series of small earthquakes does not necessarily lead to a big earthquake.
Why Italy sent seismologists to jail in 2012.
They were charged for manslaughter for downplaying the possible severity of the earthquake. There were foreshocks before, but the seismologists chose to deem no threat.
What earthquake forecasts are based on.
Earthquake forecasts rely on historical records of seismic activity in a given region to estimate the probability of an earthquake of a certain magnitude happening in a particular timeframe
How GPS measurements of surface deformation can help estimate earthquake potential.
GPS data is used to measure slip deficits — the difference between actual movement on a fault and the movement expected based on tectonic forces. Large slip deficits indicate that significant strain has accumulated and could be released in an earthquake.
When you stay inside or leave a building during an earthquake.
Stay inside if building is more physically secure
What you should do if on a high floor in a building during an earthquake.
Drop to the ground, take cover under a heavy object and wait.
How an earthquake early warning system works.
Early warning systems detect the seisemic waves, which are slower than the speed of light, and give an alert a few seconds before the earthquake
How long after surface waves arrive poorly constructed buildings generally collapse.
Within seconds of the surface waves.
The buildings that collapsed disproportionally during the 2008 Wenchuan, China Earthquake.
7,000 poorly built schoolhouses, killing around 10,000 students.
The required percent chance of avoiding collapse during a California earthquake.
90% chance of avoiding collapse
What forced resonance is.
Natural frequency of the structure matches the frequency of shaking, leading to amplified shaking and higher chance of collapse
Why diagonal beams help buildings to be more resistant to earthquakes.
Provides resistance to shearing forces
That the addition of simple corner studs can greatly improve building earthquake stability.
Distribute stress more evenly, making it more resistant to shaking
The importance of a strong foundation for a building to be earthquake resistant.
Buildings without a proper foundation are more prone to amplified shaking
What liquefaction is.
When water saturated soils lose strength, leading to the grains losing contact and more easily slide leading to physical structures on top collapsing
How an earthquake isolation system works.
Mounting them on isolators and steel that absorb side-side motion
How can the potential size of an earthquake be forecasted from the slip deficit?
Knowing how fast the slip deficit is growing and the time since the last earthquake.
